The present invention is directed to switching devices, and more particularly, to a puncture-resistant mat for pressure-actuated switches.
Various types of pressure-actuated switching devices are known in the art. Switching devices have been designed for use in many different applications including the placement in passenger seats which are actuated when a person sits in the seat, placement in street surfaces which are actuated by the passage of vehicles, placement in doormats, and for security purposes, for example, to detect the movement of heavy objects such as furniture. In certain applications, it is desirable to protect the switching device by placing the switching device within a protective mat.
Electric switches have been incorporated within several types of mats in order to protect the switches from wear and other potentially adverse effects such as moisture. Included among such mat switches are those shown in U.S. Pat. Nos. 2,938,977 to Koenig, 3,243,540 to Miller, 3,283,096 to Horton (which corresponds to Canadian patent 787,520), and U.S. Pat. No. 4,497,989 to Miller.
U.S. Pat. No. 2,938,977 to Koenig discloses an electric switching mat having a bottom sheet of insulating material, a plurality of upper and lower contact strips separated by insulating strips, and an upper sheet of insulating material placed over the strips thereby sandwiching the strips between the upper and lower sheets.
U.S. Pat. No. 3,243,540, to Miller discloses an electric mat switch incorporating compressible protective layers made of foam rubber or the like.
U.S. Pat. No. 3,283,096, to Horton discloses a mat switch having a single sealed envelope for the switch element. The membranes of the switch element are themselves relatively thick members made from glass fiber-reinforced synthetic polymer in order to prevent buckling and shorting of the contact elements.
U.S. Pat. No. 3,722,086 to Wikkerink, et al. discloses a process for making floor mat switches made of two contact plates formed of sheets of slight guage spring steel which are spaced apart by a plurality of dielectric pads. Additionally, a band of dielectric material is positioned between the peripheral edges of the contact plates.
U.S. Pat. No. 4,497,989, to Miller discloses an electric mat switch wherein two conductor layers are separated by a separator layer of PVC foam. The electric mat switch also comprises a top outer layer and a separate moisture layer formed of PVC, an upper bulking layer formed of fiberglass fabric, all of which are disposed above the conductor layers. Below the conductor layers are a corresponding lower bulking layer formed of fiberglass fabric, a lower moisture layer, and a lower outer layer.
Other types of protective mats which are used with pressure sensitive electrical-switches have been used in the art, wherein layers of sheetmetal having a thickness of about 1/16 inch form the contacts of the electrical switches, and the switches are enclosed in a moisture resistant envelope. These switches, however, suffer from several disadvantages. First, these known mats do not provide protected isolation chambers for the switches. Thus, if a sharp object comes in contact with the outer surface of the protective mat and punctures the outer envelope, moisture, dirt or other corrosive substances can easily come in contact with the switching element. Secondly, since the known mats use metal plates as the switch contacts, they are not very resistant to permanent deformation. Therefore when an object comes in contact with the mat, the sheetmetal contacts are often permanently deformed and, even after the object has been removed from the mat, the permanently deformed contacts are in a position of continuous actuation rendering the switching device useless. Furthermore, the weight of the metal plates may cause design problems when it is desired to construct a very sensitive switch. Lastly, the rigidity of the metal plates combined with the tension of the outer casing, actuates the switches if the mats are not positioned on level surfaces. Thus, the floor area or other mounting surface may need special preparation during the installation of one of these known protective mats.
The above-mentioned mats are intended for use with pressure-actuated electrical switches. Such electrical switches are well-known in the art, and have been designed for many applications. Included among the switches designed for use in passenger seats are U.S. Pat. Nos. 3,487,451 to Fontaine, 3,715,541 to Koenig, and 3,812,313 to Wolf, et al.
U.S. Pat. No. 3,487,451, to Fontaine discloses a brake controlling mechanism for placement within the seat of a vehicle having a multi-layer switch element incorporating protective layers which are made of foam rubber or the like. The entire switch assembly is sealed within an outer envelope having a multiplicity of apertures which allow the envelope to breath.
U.S. Pat. No. 3,715,541, to Koenig discloses a ribbon switch having an inner sealed switch member placed between relatively stiff cover strips which transmit flexural forces to the switch.
U.S. Pat. No. 3,812,313, to Wolf, et al., discloses an electric ribbon switch designed to maintain uniform sensitivity when the switch is in a bowed condition, e.g. in the seat of a car. The Wolf, et al. switch has two contact strips: one strip has diagonal slots to enhance flexibility and the other contact strip has corresponding portusions to increase sensitivity. In order to further increase sensitivity, the contact strips are placed in a casing having a longitudinal bead. A thin spring steel actuating strap is placed adjacent the bead in order to localize and concentrate the actuating pressure applied to the outer cover.
A switch of the type designed to detect street traffic is disclosed in U.S. Pat. No. 1,950,490, to Geer, et al., which shows a membrane switch encapsulated in several layers of material and installed in a structure provided with a protective elastomeric treadle member.
Switches which may be used in doorways are disclosed in U.S. Pat. Nos. 4,293,752 to Koenig and 4,551,595 to Koenig, et al.
U.S. Pat. No. 4,293,752 to Koenig discloses a self-adhering tapeswitch comprising a conventional pair of electrical contacts separated by a pair of insulating strips, all of which are enclosed within a plastic cover. A layer of deformable material is bonded to the underside of the plastic cover. A strip of pressure sensitive adhesive is mounted on the underside of the deformable material and the adhesive is covered by a removable paper strip The paper strip is removed when it is desired to contact the adhesive with a surface.
U.S. Pat. No. 4,551,595 to Koenig, et al., discloses an electrical switch having a corrugated wavy conductor comprising an upper insulating cover strip to which is bonded a corrugated conductor strip. A corresponding bottom cover strip has a generally flat conductive strip. A pair of insulating spacer strips are mounted between the cover strips.
An example of a normally-closed pressure switch is shown in U.S. Pat. No. 3,553,404 to Koenig which discloses a ribbon switch wherein elongated, transversely curved spring-type conductive members are confined between stiffener plates and the assembly is enclosed in a sealed flexible casing.
A switch designed particularly for isolation from the environment is shown in U.S. Pat. No. 4,237,358, to Larson, et al., which discloses a membrane switch having two spaced membranes provided with facing conductive elements. The switch is provided with a "pressure reduction membrane" positioned in contact with the upper switch membrane and an additional isolation membrane superimposed on the pressure reduction membrane.
Protective mats for pressure-sensitive switches such as those described above have been useful, however, they fail to provide the degree of resistance to damage by impact and puncture by sharp objects which is desired in certain applications such as when the switch is to be used near sharp heavy objects or tools which are likely to fall on the mat.